This reverts commit 36e3b103 to make the build green.

SDK now includes the following versions:

* Tools: 25.2.5
* Platform Tools: 27.0.1
* Build Tools: 27.0.3
* Android 6.0 (API 23)
* Android Support Repo: 47
* Google Play Services: 46

This started breaking the analyzer following https://github.com/flutter/flutter/pull/13889
The test version of the material_animated_icons did not include the meta
package (needed for the @required tag) and was also not including all
the generated icons files.

Ideally we should find a way to fix this without enumerating all the
icons in the test file.
But for now just adding the missing file to fix the build breakage.

This reverts commit b56295aa.

This reverts commit 25b1d43a.

* modernize capability names in devicelab task manifest

* replace windows too

* Roll engine to 37789650cb1254199426e5de5cc66c2ba63cbaf2
* Fix large integer literals in packages/flutter/test/services/message_codecs_test.dart

Try again now since texture-related test-breaking PR was backed out.

Fixes #13743 
Fixes #12379
Follow-up to #13745

Also adds an option to hide gestures introduced by `InkWell` and `InkResponse` from the semantics tree (see also `GestureDetector.excludeFromSemantics`).

Reformats a SafeArea introduced in #13853.

* Remaining code changes for Dart 2.0 SDK roll

Applies horizontal safe area insets to the animation demo in the
Gallery. Specifically, this ensures the back button is positioned
consistently with iOS expectations and that that main image card in the
detail view respects safe area insets.

This is to support the iPhone X sensor housing notch and other similarly
creative display features when in landscape orientation.

Applies horizontal safe area insets to the video demo in the Gallery.
This is to support the iPhone X sensor housing notch and other similarly
creative display features when in landscape orientation.

* Revert "Roll engine to e122f4825726035e4579471ef83848b1aa796444 dart roll"

This reverts commit c7dfadfa.

* Revert "Roll engine to just before dart roll"

This reverts commit d5cc8657.

* Revert "Revert "Enable developers to run pod from terminal directly and skip pod install if possible. (#13374)" (#13770)"

This reverts commit 0759043e.

* some nits on cocoapods code

* put back the FLUTTER_FRAMEWORK_DIR env variable

Revert "Enable developers to run pod from terminal directly and skip pod install if possible. (#13374)" (#13770)

This reverts commit c6a17525.

Avoids running pod install if .flutter-plugins and its flutter framework pod dependency didn't change

Executables have '.exe' extension on Windows. We do have to specify extension for gen_snapshot since when running with local engine, we are looking for that exact file before launching it.

This reverts the change to `user_accounts_drawer_header.dart`
(and the associated test), as it was causing regressions in layout
of the drawer header.

https://github.com/flutter/flutter/issues/13743

* Create CupertinoScrollbar

* handle main axis margin

* Adaptive material scrollbar and tests

* Small tweaks

* reapply changes on head

* Docs

* start

* Refactored ScrollbarPainter to be more immutable

* fix tests

* fix bug: one animationcontroller pointed to multiple painters

* some docs tweak

* remove unused import

* review

* review

* add dispose

**tl;dr:** A `RenderObject` can only be an effective semantics boundary if it actually owned a `SemanticsNode` in the previous tree generation.

When using the `BlockSemantics` widget it is possible to introduce `RenderObject`s that are configured to be a semantics boundary, but because their semantics are blocked by `BlockSemantics` they will not (immediately) end up owning a `SemanticsNode`. When now a descendant of such a node-less semantics boundary marks itself as needing a semantics update we walk up the tree until we find the closest semantics boundary (which is our node-less `RenderObject`). We now incorrectly assume that this semantics boundary has a valid `SemanticsNode` and only regenerate the semantics subtree below this node. However, because the identified semantics boundary doesn't actually own a valid `SemanticsNode` asserts are throwing (e.g. `Child with id xx is invisible and should not be added to tree.`).

To fix this problem, we can just abort the walk if we reach a semantics boundary without a semantics node because (for now) we know that the semantics information of this branch will not make it into the final semantics tree.
If the semantics block is ever removed, the current algorithm re-generates the semantics for the entire branch and the semantics will be up-to-date then despite the abort. I've added a test to verify this to make sure it continues to work even when we change the algorithm.

Fixes https://github.com/flutter/flutter/issues/13326.
/cc @gavindoughtie FYI

This attempts to apply some of what we learnt from UX studies, namely
that people wonder how to add multiple children to widget that take
one child.

This is a collection of fixes I've run into recently.